Process for preparing (+)-2,3-dihydro-1H-pyrrolo[1,2-A]pyrrole-1,7-dicarboxylates

ABSTRACT

2,3-Dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylates of the formula, ##STR1## in which each R is independently H or lower alkyl, are prepared from di(lower alkyl) 1,3-acetonedicarboxylates.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of our copending U.S. patent application Ser. No. 003,104, filed Jan. 14, 1987 now U.S. Pat. No. 4,849,526.

This application is related to the subject matter of our copending and commonly assigned U.S. patent application Ser. No. 07/003,162, filed Jan. 14, 1987, for "Process for Preparing (±)-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylates", now U.S. Pat. No. 4,835,288 which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pyrrolo[1,2-a]pyrroles, and especially to the synthesis of 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylic acid and its dialkyl esters.

2. Background to the Invention

5-Aroyl-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acids, also known as 5-aroyl-2,3-dihydro-1H-pyrrolizine-1-carboxylic acids, of formula I, and the ##STR2## pharmacologically acceptable salts and esters thereof, are useful as analgesic, anti-inflammatory, and anti-pyretic agents for mammals, including man. They are also smooth muscle relaxants. Two exemplary compounds under clinical study in man are ketorolac, 5-benzoyl-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid, (I, Ar=C₆ H₅), and anirolac, 5-p-anisoyl-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid, (I, Ar=p--CH₃ O--C₆ H₅), both disclosed in U.S. Pat. No. 4,089,969 to Muchowski et al. Other compounds where the 5-aroyl substituents are sustituted or unsubstituted benzoyl, furoyl, thenoyl, and pyrroyl, and where the 6-position on the pyrrolo-pyrrole nucleus is optionally substituted by lower alkyl or halogen, and the uses thereof, are also disclosed in a series of patents assigned to Syntex (U.S.A.) Inc., beginning with U.S. Pat. No. 4,089,969, and including U.S. Pat. Nos. 4,087,539; 4,097,579; 4,140,698; 4,232,038; 4,344,943; 4,347,186; 4,458,081; 4,347,187; 4,454,326; 4,347,185; 4,505,927; 4,456,759; 4,353,829; 4,397,862; 4,457,941; and 4,454,151. U.S. Pat. Nos. 4,511,724 and 4,536,512, assigned to Merck & Co., Inc., disclose 5-(substituted pyrrol-2-oyl)-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid derivatives and 5-(2,3-dihydro-1H-pyrrolo[1,2-a]pyrrol-2-oyl)-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid derivatives, respectively; while U.S. Pat. No. 4,533,671, also assigned to Merck & Co., Inc., discloses 5-(2,3-dihydro-1H-pyrrolo[1,2-a]pyrrol-2-oyl)-2-pyrrolealkanoic acids and analogs.

Various methods for the preparation of these pyrrolo-pyrroles are exemplified in the patent and chemical literature, and many proceed through a common intermediate, 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylic acid, (II, R=H), or its dialkyl ester; ##STR3## the preparation of which from dimethyl 1,3-acetonedicarboxylate, ethanolamine, and a haloacetaldehyde is disclosed in, for example, U.S. Pat. No. 4,089,969, which is incorporated herein by reference.

The reaction scheme set forth in that patent: ##STR4## includes the reaction of equimolar amounts of ethanolamine (III) and dimethyl 1,3-acetonedicarboxylate (IV) to form a solution of the hydroxyenamine (V), which is then treated, preferably in situ, in a suitable organic solvent (aprotic solvents such as acetonitrile, dichloromethane, etc. are exemplified) under anhydrous conditions, with a 2-haloacetaldehyde at elevated temperatures to produce the N-(2-hydroxyethyl)pyrrole (VI). Compound VI is esterified with methanesulfonyl chloride to produce the mesylate (VII), which is optionally converted to the N-(2-iodoethyl)pyrrole (VIII) by reaction with sodium iodide. Either of compounds VII and VIII may be converted to dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate (II, R=CH₃) by treatment with sodium hydride in dimethylformamide. The thus-formed dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate may then be selectively 7-decarboxylated and 5-aroylated, by methods such as those described in the previously-cited patents and in U.S. Pat. No. 4,496,741 to Doherty, to yield a 5-aroyl-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid (I). A similar process, involving the reaction of ethanolamine, dimethyl 1,3-acetonedicarboxylate, and a halomethyl alkyl ketone, bypasses the hydroxyenamine (V) and produces the 4-alkyl analog of (VI) directly. That compound may be converted to the pyrrolo-pyrrole in the same manner as for the 4-unsubstituted compound previously described.

Processes for the preparation of 5-aroyl-N-R-pyrrole-2-acetic acid, where R is H, lower alkyl, or benzyl, and analogous compounds are disclosed in U.S. Pat. Nos. 3,752,826; 3,865,840; and 3,952,012 to Carson. They include, for the 4-alkyl substituted but not for the 4-unsubstituted compounds, the reaction between a lower alkylamine, a di(lower alkyl) 1,3-acetonedicarboxylate, and a chloromethyl lower alkyl ketone, "preferably in an aqueous medium", followed by pouring into ice-cold hydrochloric acid, to produce compounds of formula IX, where each of R, R', and R" is lower alkyl. ##STR5## A similar process for the 4-unsubstituted compounds (IX, R'=H) using chloroacetaldehyde is disclosed in U.S. Pat. No. 4,048,191 to Carson.

U.K. Published Application No. 2 034 304 A, assigned to Mallinckrodt, Inc., discloses a process for the preparation of compounds of formula IX, wherein R' may be hydrogen or alkyl, by either (a) forming a two-phase reaction medium of an aqueous solution of the alkylamine and an inert, water-immiscible organic solvent, and adding the dicarboxylate and ketone (or aldehyde) substantially simultaneously, or (b) adding the dicarboxylate and ketone substantially simultaneously, with the ketone in excess, to an aqueous alkylamine. Preferably, dicarboxylate and excess ketone are added to an alkylamine dispersion.

A number of patents assigned to Ethyl Corporation, including U.S. Pat. Nos. 4,565,878; 4,565,879; 4,374,255; 4,388,468; 4,383,117; 4,455,433; and 4,333,878, disclose other modifications of the Carson syntheses. U.S. Pat. No. 4,565,878 discloses the addition of a water-immiscible co-solvent [a halogenated hydrocarbon of good solubility for both the di(lower alkyl) 1,3-acetonedicarboxylate and the product] to the mixture of chloromethyl lower alkyl ketone, dicarboxylate, and aqueous lower alkylamine. U.S. Pat. No. 4,565,789 discloses the use of an aromatic hydrocarbon as the co-solvent. U.S. Pat. No. 4,374,255 discloses the addition of "a solids formation inhibiting amount of a lower alkanol" to the ketone/dicarboxylate/aqueous alkylamine mixture. The reaction is normally carried out in the presence of a co-solvent as in U.S. Pat. Nos. 4,565,878 or 4,565,879. U.S. Pat. No. 4,388,468 discloses a two-stage process in which (a) the ketone is added to a pre-mixed cooled solution of the alkylamine and the dicarboxylate in a suitable solvent (e.g. aromatic hydrocarbons, chlorinated hydrocarbons, water, or mixtures thereof) at a temperature less than 60° C., followed by (b) heating the reaction mixture to 70°-100° C. U.S. Pat. No. 4,383,117 discloses the use of an anhydrous lower alkylamine instead of an aqueous solution, and the use of a single-phase non-aqueous reaction medium. U.S. Pat. No. 4,455,433 discloses the addition of "a yield-enhancing amount of an acid having a dissociation constant of at least 1.3×10⁻⁵ at 25° C." to a ketone/dicarboxylate/(preferably anhydrous) lower alkylamine mixture, preferably in an organic solvent. U.S. Pat. No. 4,333,878 discloses the synthesis of compounds of formula IX by the reaction of an enamine (X) ##STR6## with a 2-carboxyl-nitroalkane (IX, R*=lower alkyl, tolyl, or benzyl). The enamine may be prepared by the reaction of a di(lower alkyl) 1,3-acetonedicarboxylate with a lower alkylamine in "a suitable solvent, such as ethanol or methanol", followed by evaporation of the solvent and heating to dehydrate the thus-formed carbinolamine to the corresponding enamine.

Albert et al., in U.S. Pat. No. 4,363,918, disclose the synthesis of compounds of formula IX where R is lower alkyl, R' is hydrogen or lower alkyl, and R" is H by the reaction of 1,3-acetonedicarboxylic acid with ClCH₂ COR nd a lower alkylamine, preferably by the slow addition of an aqueous solution of the lower alkylamine to an aqueous solution of the acid, followed by slow addition of the 1-chloro-2-alkanone, with both additions preferably occurring below 20° C. or lower.

European Published Applications Nos. 92 487 and 105 664, assigned to Montedison S.p.A., disclose the preparation of compounds of formula IX wherein R is CH₃ and R" is H, and R' is CH₃ (EP92487) or H (EP105664) by the reaction of 1,3-acetonedicarboxylic acid or an alkali metal salt thereof with methylamine and a halo(ketone or aldehyde) in aqueous solution, preferably by adding the haloketone to an aqueous mixture of the methylamine and the dicarboxylic acid.

SUMMARY OF THE INVENTION

In a first aspect, this invention relates to the preparation of 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylates of formula XII, ##STR7## in which

each R is independently H or lower alkyl, from di(lower alkyl) 1,3-acetonedicarboxylates.

The preparation may be represented schematically: ##STR8## in which

R is as previously defined;

Ms is mesyl; and

X is halogen.

In a second aspect, this invention relats to novel compounds of formula XVI, which are useful as intermediates in the process herein.

DETAILED DESCRIPTION OF THE INVENTION Definitions

Unless otherwise stated, the following terms used in the specification and claims have the meanings given below:

"lower alkyl", denoted generally by R (which may also denote hydrogen, though that is not "lower alkyl"), refers to straight, branched, or cyclic saturated hydrocarbon radicals having from one to six carbon atoms, e.g. methyl, ethyl, isopropyl, cyclopropylmethyl, pentyl, cyclohexyl, and the like. Preferred lower akyls are methyl, ethyl, and n-propyl, and a particularly preferred lower alkyl is methyl. If more than one alkyl radical is present in a given molecule, each may be independently selected from 37 lower alkyl" unless otherwise stated.

"lower alkoxide", "lower alkanol", "lower alkylamine", "lower alkyl ester", and similar terms refer to alkoxides, alkanols, alkylamines, alkyl esters, etc. in which the (or each) alkyl radical is a "lower alkyl" as defined above.

"halogen", denoted generally by X, refers to chlorine, bromine, or iodine. Preferred halogens are chlorine and bromine.

"aprotic polar solvent" includes organic solvents which may be either water-immiscible, such as halogenated hydrocarbons, e.g. methylene chloride, chloroform, etc., or water-immiscible, such as tetrahydrofuran, dimethoxyethane, bis(2-methoxyethyl) ether (diglyme), dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, etc. the solvent may also contain minor proportions of aprotic non-polar solvents such as hydrocarbons, e.g. cyclohexane, toluene, and the like, provided that the solvent properties are largely determined by the polar solvent.

"weak base" refers to the alkali metal or alkaline earth salt of a weak acid, e.g. sodium acetate, potassium bicarbonate, etc., or to a buffer mixture (such as NaH₂ PO₄ /Na₂ HPO₄) giving a similar pH.

"strong base" refers to bases such as alkali metal hydroxides, lower alkoxides, hydrides, di(lower alkyl)amines, and the like, e.g. sodium hydroxide, potassium methoxide, sodium hydride, lithium di(isopropyl)amine, lithium bis(trimethylsilyl)amine, etc.

"mesyl", denoted by Ms, refers particularly to methanesulfonyl, but includes other equivalent alkyl- or arylsulfonyls, such as ethanesulfonyl, benzenesulfonyl, p-toluenesulfonyl, and the like.

"water-miscible co-solvent" includes lower alkanols, di(lower alkyl) ketones, tetrahydrofuran, dioxane, sulfolane, dimethylformamide, and the like. Preferred co-solvents are methanol, acetone, and similar C₁ or C₂ alkyl alcohols and ketones.

Starting Materials and Purification

Dimethyl 1,3-acetonedicarboxylate is commercially available (Aldrich), as is 1,3-acetonedicarboxylic acid, also known as 3-oxopentanedioic acid. Other di(lower alkyl) 1,3-acetonedicarboxylates may readily be prepared from either the dimethyl ester or, preferably, the diacid, by esterification techniques well-known to the art. However, there is no particular advantage in varying the alkyl groups, so that the dimethyl ester is preferred.

The starting materials and the intermediates of formulae XIII, XIV, XV, and XVI may be isolated if desired, using conventional techniques, including but not limited to filtration, distillation, crystallization, chromatography and the like. Such materials may be characterized using conventional means, including physical constants and spectral data.

Preparation of Compounds of Formula XII

In Step 1, a di(lower alkyl) 3-(2-haloethylamino)-2-pentenedioate ("haloenamine") is prepared from a di(lower alkyl) 1,3-acetonedicarboxylate, either by direct reaction with a 2-haloethylamine hydrohalide salt, or by reaction with 2-hydroxyethylamine (2-aminoethanol) followed by replacement of the hydroxy group by a halide.

In Alternate I (which is preferred), the di(lower alkyl) 1,3-acetonedicarboxylate is treated with a 2-haloethylamine hydrohalide salt in aqueous solution. The solution preferably has a pH between 5 and 12, more preferably between 5 and 8. Typically, the pH is controlled by employing an aqueous solution of a weak base, such as sodium acetate, as the reaction solvent, but other methods may be employed, if desired. The reactants may be added simultaneously or consecutively, as desired, but it is desirable that the 2-haloethylamine hydrohalide not be placed in basic solution unless that solution already contains the acetonedicarboxylate, to avoid the formation of aziridines. Typically, the 2-haloethylamine hydrohalide and acetonedicarboxylate are dissolved, either simultaneously or in the order stated, in water, and a solid weak base added to produce the reaction mixture. The reaction is preferably conducted at a temperature between 0° and 35° C., more preferably at about room temperature, i.e. between about 15° and 30° C.; over a time preferably between about 30 minutes and 24 hours, more preferably between about 4 and 18 hours. The intermediate di(lower alkyl) 3-(2-haloethylamino)-2-pentenedioate ("haloenamine") typically crystallizes and may be isolated by filtration, as a mixture of the E and Z isomers. Each R is preferably methyl, X is preferably bromine or chlorine, and a sodium acetate is preferably used to control pH.

In Alternate II, the di(lower alkyl) 1,3-acetonedicarboxylate is treated with 2-hydroxyethylamine (2-aminoethanol) in an aprotic polar solvent to produce the hydroxyenamine (XIV), which is then converted to the haloenamine (XIII) via the mesylenamine (XV). The conversion may stop at the mesylenamine stage, and the mesylenamine be cyclized directly (Step 2, Alternate II) if desired. Typically, the dicarboxylate is dissolved in the solvent, the 2-hydroxyethylamine is added slowly to the resulting solution, and the water formed during the reaction is removed by azeotropic distillation. While the hydroxyenamine may be formed under less stringent conditions (see, e.g., U.S. Pat. No. 4,089,969), an anhydrous solution of the hydroxyenamine is required for the next reaction, and it is therefore convenient to carry out the formation of the hydroxyenamine in an aprotic medium. The resulting solution contains a mixture of the E and Z isomers of the hydroxyenamine, and may be used without purification in the next step. As in Alternate I, a preferred R is methyl. A preferred solvent is dichloromethane.

Esterification of the hydroxyenamine (XIV) with mesyl chloride in the presence of an organic base such as a tertiary amine, optionally in the presence of an aprotic polar solvent, takes place at a temperature between about -10° C. and room temperature, preferably between about 0° and 10° C. Conveniently, the tertiary amine is added to the solution from the previous reaction, which has been cooled to the appropriate temperature, and the mesyl chloride is added slowly to the resulting solution over a period between about 30 minutes and 10 hours, typically about 2 to 5 hours. The solution of the resulting mesylenamine (XV) is quenched with water, and solvent removed from the organic phase to afford a mixture of the E and Z isomers of the mesylenamine (XV), which may be used without further purification in the next reaction, though purification is preferable if the mesylenamine is to be cyclized directly rather than to be first converted to the haloenamine.

The mesylenamine (XV) is converted into the corresponding haloenamine (XIII) by reaction with an anhydrous alkali halide, preferably a bromide or iodide, e.g. sodium iodide, lithium bromide, etc., in an aprotic polar solvent at a temperature between about room temperature and the reflux temperature of the solvent, e.g. between about 30° and 100° C., for 1 to 30 hours, e.g. between 5 and 20 hours, the period depending on the reagents and reaction temperature. The haloenamine (XIII) may be readily isolated by adding water to the reaction mixture, washing the organic phase, and removing the solvent to afford a mixture of the E and Z isomers of the haloenamine, which may conveniently be purified by recrystallization.

Preparation of Compounds of Formula XII

In Step 2, the haloenamine (XIII) or mesylenamine (XV) from Step 1 is cyclized with a strong base in an aprotic polar solvent.

In Alternate I (which is preferred), typically the haloenamine is dissolved in the solvent, and from 1 to 2 equivalents, preferably from 1.1 to 1.5 equivalents, of the strong base added in solid form. If the base is not soluble in the solvent, it may be desirable to add a phase-transfer catalyst, such as a tetraalkylammonium halide, etc., to enhance the rate of reaction. The reaction occurs preferably between about 15° and 35° C., more preferably at about room temperature, over from about 1 to 30 hours. The resulting cyclic enamine (XVI) may be isolated, for example by water extraction of the solution and evaporation of the solvent, and may conveniently be purified by distillation (e.g. Kugelrohr) and/or recrystallization. The E and Z isomers may be separated, if desired, but it is unnecessary to do so, as they both react in Step 3. X is preferably Br; and preferred strong bases and solvents are sodium methoxide in dichloromethane, sodium hydroxide in tetrahydrofuran or dimethylsulfoxide, sodium hydride in tetrahydrofuran, etc.

In Alternate II (cyclization of the mesylenamine (XV)), a similar process to that described above is performed, but the quantities of base employed are generally larger, e.g. up to 6 equivalents based on the mesylenamine, and the reaction conditions more stringent (higher temperatures, e.g. up to solvent reflux temperature, and longer times). A preferred base/solvent combination is aqueous sodium hydroxide/dichloromethane, using a phase transfer catalyst.

In Step 3, the pyrrole ring of the pyrrolo-pyrrole is formed by reaction of the cyclic enamine (XVI) with a 2-haloacetaldehyde, XCH₂ CHO, where X is as previously defined. The process is preferably conducted in aqueous solution at a pH between 4.5 and 10, preferably between 5 and 8.5. The reaction is preferably carried out between 15° and 35° C., more preferably at about room temperature, for from about 1 to 10 hours, preferably between 2 and 5 hours. X is preferably Br, and pH control is preferably achieved by the presence of a weak base, e.g. sodium acetate or sodium bicarbonate, in the solution. The process is preferably carried out in the presence of 10 to 50 volume percent of a water-miscible co-solvent, such as methanol.

Typically, the cyclic enamine (XV) is added to an aqueous solution of the 2-haloacetaldehyde and a weak base. A water-miscible co-solvent is preferably also added. The mixture is stirred for the appropriate time, and the resulting compound of formula XII may be isolated from the reaction mixture, e.g. by evaporation of the solvent, and purified as desired. The 2-haloacetaldehyde may be obtained commercially or prepared by any desired route. In the case of the preferred 2-bromoacetaldehyde, exemplary preparative methods include the acid hydrolysis of a 2-bromoacetaldehyde di(lower alkyl) acetal, a lower alkyl 1,2-dibromoethyl ether, 1,2-dibromoethyl acetate, etc., each of which results in an aqueous solution of 2-bromoacetaldehyde.

If the dicarboxylic acid (XII, R=H) is desired, (XII) may be saponified by conventional chemical means, e.g. reaction with a strong base to remove the ester groups and treatment with acid to generate the dicarboxylic acid. The diester is dissolved in an aqueous alkali metal hydroxide or carbonate solution, e.g., sodium hydroxide solution, which may also contain a water-miscible co-solvent, e.g., methanol, at a temperature between about room temperature and the solvent reflux temperature for from about 30 minutes to 24 hours, e.g. 1 to 4 hours. The cooled solution is then acidified with an aqueous strong acid, e.g. 35% hydrochloric acid, and the dicarboxylic acid precipitates and may be removed by filtration. The dicarboxylic acid may be purified by conventional means, especially conveniently by recrystallization from aqueous solution.

The C-1 acid group of the resulting dicarboxylic acid (XII, R=H) may then be selectively esterified, and the 1-ester-7-acid decarboxylated to afford the pyrrolo-pyrrole-1-carboxylate, which may be 5-aroylated to afford compounds of formula I, all by methods described in the patents set forth in the "Background to the Invention" section of this application, e.g. U.S. Pat. No. 4,089,969.

EXAMPLES

The following Examples illustrate this invention, but are not intended to limit its scope.

EXAMPLE 1 Preparation of dimethyl 3-(2-bromoethylamino)-2-pentenedioate. (Step 1, Alternate I)

A. 2-Bromoethylamine hydrobromide (12.35 g, 60 mmol) was dissolved in water (30 mL) at room temperature (20° C.) with stirring, and dimethyl 1,3-acetonedicarboxylate (10.0 g, 57 mmol) was added. After 5-10 minutes, solid anhydrous sodium acetate (14.35 g, 175 mmol) was added, and stirring continued. After approximately 80 minutes, precipitation of dimethyl 3-(2-bromoethylamino)-2-pentenedioate began, and the solution was stirred for 17 hours at room temperature. The thick slurry was diluted with cold water (20 mL), and aged at 0°-5° C. for 30 minutes and filtered, and the precipitate washed with cold (0°-5° C.) water (50 mL) and dried to constant weight, to afford 13.9 g (86% yield) of dimethyl 3-(2-bromoethylamino)-2-pentenedioate as a white solid, m.p. 71°-72° C.

B. Substituting 2-chloroethylamine hydrochloride (7.0 g, 60 mmol) for the 2-bromoethylamine hydrobromide in the procedure of part A of this Example, there was obtained 10.8 g (80% yield) of dimethyl 3-(2-chloroethylamino)-2-pentenedioate as a white solid, m.p. 75°-76° C.

C. Substituting for dimethyl 1,3-acetonedicarboxylate in the procedure of parts A or B of this Example,

diethyl 1,3-acetonedicarboxylate,

dipropyl 1,3-acetonedicarboxylate,

di(i-propyl) 1,3-acetonedicarboxylate,

di(t-butyl) 1,3-acetonedicarboxylate, or

dihexyl 1,3-acetonedicarboxylate,

one obtains, respectively,

diethyl 3-(2-bromoethylamino)-2-pentenedioate,

dipropyl 3-(2-bromoethylamino)-2-pentenedioate,

di(i-propyl) 3-(2-bromoethylamino)2-pentenedioate,

di(t-butyl) 3-(2-bromoethylamino)-2-pentenedioate,

dihexyl 3-(2-bromoethylamino)-2-pentenedioate,

diethyl 3-(2-chloroethylamino)-2-pentenedioate,

dipropyl 3-(2-chloroethylamino)-2-pentenedioate,

di(i-propyl) 3-(2-chloroethylamino)2-pentenedioate,

di(t-butyl) 3-(2-chloroethylamino)2-pentenedioate, or

dihexyl 3-(2-chloroethylamino)-2-pentenedioate.

EXAMPLE 2 Preparation of dimethyl 3-(2-bromoethylamino)-2-pentenedioate. (Step 1, Alternate II)

A. Dimethyl 1,3-acetonedicarboxylate (196.1 g, 1.13 mol) was placed in a 3 L three-neck flask containing a stirrer bar and fitted with a thermometer, a water extractor on a reflux condenser, and an addition funnel; and the flask then purged with nitrogen. The extractor was filled with dichloromethane, and dichloromethane (800 mL) added to the flask. Ethanolamine (68.8 g, 1.13 mol) was added via the addition funnel over 10 minutes, and the mixture warmed to 30° C. The mixture was then heated under reflux for 24 hours, by which time thin-layer chromatography indicated that very little residual dicarboxylate remained and 20 mL water had collected in the extractor.

The solution of dimethyl 3-(2-hydroxyethylamino)-2-pentenedioate was cooled to 0° C., and triethylamine (235 mL, 170.6 g, 1.69 mol) was added in one portion. Methanesulfonyl chloride (168.8 g, 1.47 mol) was added dropwise via an addition funnel over 3.75 hours, with the temperature rising to 5°-7° C. The medium-yellow slurry darkened to yellow-orange as the last 10 mL methanesulfonly chloride was added. The mixture was stirred at 0° C. for an additional 2 hours, and water (250 mL) added. The organic phase was washed with water (4×500 mL) and brine (250 mL), and dried overnight over anhydrous magnesium sulfate. Afer filtration, the solvents were evaporated on a rotary evaporator under reduced pressure at 50° C. to afford 310.0 g (93% yield) of dimethyl 3-(2-methanesulfonylethylamino)-2-pentenedioate as a red oil. The mesylenamine may be purified at this point, if necessary or desired, and may be converted to the haloenamine by the following method or used directly in Step 2, Alternate II.

Dimethyl 3-(2-methanesulfonylethylamino)-2-pentenedioate (156.3 g, 529 mmol) was added to a 2 L three-neck flask, which was fitted with a mechanical stirrer, thermometer, and reflux condenser. Dichloromethane (750 mL) was added and stirred until the mesylate had completely dissolved, anhydrous lithium bromide (69.0 g, 794 mmol) was added, and the mixture stirred at 35° C. for 19 hours. The mixture was cooled to 0° C. and water (250 mL) added, then stirred for 5 minutes and the phases separated. The organic phase was washed with water (3×250 mL) and brine (150 mL), and dried over anhydrous potassium carbonate for 15 minutes. Rotary evaporation of the solvent under reduced pressure (50° C.) gave 128.4 g of crude dimethyl 3-(2-bromoethylamino)-2-pentenedioate as a yellow oil, which quickly solidified to a yellow solid. The crude material was purified by extraction into boiling hexane (5×750 mL) and recrystallization from hexane, and the pot residues extracted and recrystallized, to give a total of 90.8 g (61.2% yield) of dimethyl 3-(2-bromoethylamino)-2-pentenedioate as white needles. An NMR spectrum in CDCl₃ indicated an Z/E isomer ratio of 19:1, and remeasurement of the CDCl₃ solution after three days indicated an Z/E ratio of 4:1. The two isomers were not separated.

B. In a similar manner to that of part A of this Example, using sodium iodide in place of lithium bromide, and acetone or acetonitrile in place of dichloromethane, there was obtained in each instance crude dimethyl 3-(2-iodoethylamino)-2-pentenedioate as a light brown oil, which could be purified by conventional methods.

C. Substituting lithium chloride for lithium bromide, and using a similar procedure to that in part A of this Example, one obtains

dimethyl 3-(2-chloroethylamino)-2-pentenedioate.

D. Similarly, using other di(lower alkyl) 1,3-acetonedicarboxylates in the procedures of parts A through C of this Example, one obtains other di(lower alkyl) 3-(2-haloethylamino)-2-pentenedioates.

EXAMPLE 3 Preparation of methyl 3-methoxycarbonyl-2-pyrrolidinylidenecarboxylate. (Step 2)

A. (Alternate I) Dimethyl 3-(2-bromoethylamino)-2-pentenedioate (5.00 g, 17.8 mmol) was added to a 100 mL flask containing a stirrer bar. Dichloromethane (50 mL) was then added, and the mixture stirred until complete dissolution occurred. Sodium methoxide (1.92 g, 35.5 mmol) was added in portions over 18 minutes, with some heat evolution. The reaction mixture was stirred at room temperature for 23 hours, then extracted with water (4×50 mL) and brine (50 mL) and dried over anhydrous magnesium sulfate. Rotary evaporation of the solvents gave 2.27 g of a pale yellow solid, which was separated by preparative thin-layer chromatography into three components. The major product was recrystallized from hexane to afford crystalline methyl (Z)-3-methoxycarbonyl-2-pyrrolidinylidenecarboxylate, m.p. 84°-85° C., NMR (CDCl₃):

δ: 7.8-8.0 (1H, broad singlet) 4.70 (1H, doublet, J=0.67 Hz) 3.75 (3H, singlet) 3.64 (3H, singlet) 3.5-3.8 (3H, multiplet) 2.1-2.5 (2H, multiplet).

A minor product was isolated as an oil, methyl (E)-3-methoxycarbonyl-2-pyrrolidinylidenecarboxylate, NMR (CDCl₃): δ: 7.8-8.0 (1H, broad singlet) 4.64 (1H, singlet) 4.08 (1H, doublet, J=11 Hz) 3.77 (3H, singlet) 3.65 (3H, singlet) 3.55 (1H, doublet, J=11 Hz) 3.5-3.9 (1H, multiplet) 2.0-2.4 (2H, multiplet).

A very minor product was also isolated as an oil, dimethyl 3-(1-aziridinyl)-2-pentenedioate.

B. (Alternate I) To a solution of dimethyl 3-(2-chloroethylamino)-2-pentenedioate (4.71 g, 20 mmol) in dichloromethane (50 mL) was added sodium methoxide (1.62 g, 30 mmol) in four equal portions over 45 minutes at room temperature. The reaction mixture, which had developed some yellow color and precipitate, was stirred for 27 hours, then worked up as described in part A of this Example to yield 2.8 g of a yellow oil, which was determined by preparative thin-layer chromatography and NMR to contain methyl (Z)- and (E)-3-methoxycarbonyl-2-pyrrolidinylidenecarboxylates.

C. (Alternate I) To a solution of dimethyl 3-(2-iodoethylamino)-2-pentenedioate (3.3 g, 10 mmol) in tetrahydrofuran (distilled, 20 mL) was added tetrabutylammonium bromide (0.32 g, 1 mmol) and sodium hydroxide beads (0.41 g, 10.3 mmol), and the resulting mixture stirred at room temperature for 5.5 hours, during which it developed a lime color. Dichloromethane (30 mL) and water (20 mL) were added, and the mixture stirred for 5 minutes, giving a light brown upper aqeous layer and a pale yellow lower organic layer. The organic layer was separated, and the aqueous layer washed with dichloromethane (2×20 mL). The washings were combined with the organic layer, and the combined organic phase washed with water (2×20 mL) and brine (20 mL). Removal of the solvents by rotary evaporation gave 1.8 g (90% yield) of a light brown oil, which solidified on standing. Thin-layer chromatography and NMR spectra indicated major and minor proportions of methyl (Z)- and (E)-3-methoxycarbonyl-2-pyrrolidinylidenecarboxylates, with a very minor proportion of the elimination product dimethyl 3-(vinylamino)-2-pentenedioate.

D. (Alternate I) Similarly, using other di(lower alkyl) 3-(2-haloethylamino)-2-pentenedioates and, optionally, other strong bases and/or aprotic polar solvents, in the procedures of parts A through C of this Example, one obtains other (lower alkyl) 3-(lower alkoxy)carbonyl-2-pyrrolidinylidenecarboxylates.

E. (Alternate II) To a nitrogen-purged three-neck 1 L flask containing a spin bar and fitted with a reflux condenser were added sodium hydroxide (32.00 g, 800 mmol) and water (32.0 mL), and these were stirred until complete solution was obtained. Dichlormethane (640 mL) was then added, followed by dimethyl 3-(2-methanesulfonylethylamino)-2-pentenedioate (40.12 g, 136 mmol) and tetrabutylammonium bromide (6.57 g, 20 mmol). The reaction mixture was heated at reflux for 7 hours, at which time thin-layer chromatography revealed the presence of a small quantity of starting mesylenamine. The reaction mixture was therefore stirred for a further 14 hours at room temperature, at which time thin-layer chromatography showed no mesylenamine remaining, then washed with water (3×200 mL) and brine (200 mL), and dried over anhydrous magnesium sulfate to afford a yellow solution. Rotary evaporation of the solvent under reduced pressure gave a red, mobile liquid, which was distilled (Kugelrohr, 0.3 mm Hg, 50°-55° C.) to afford 19.74 g (72.9% yield, distilled) of a mixture of methyl (Z)- and (E)-3-methoxycarbonyl-2-pyrrolidinylidenecarboxylates as a clear, colorless oil.

F. (Alternate II) Similarly, using other di(lower alkyl) 3-(2-methylethylamino)-2-pentenedioates and, optionally, other strong bases and/or aprotic polar solvents in the procedure of part E of this Example, one obtains other (lower alkyl) 3-(lower alkoxy)carbonyl-2-pyrrolidinylidenecarboxylates.

EXAMPLE 4 Preparation of dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate. (Step 3)

A. 2-Bromoacetaldehyde dimethyl acetal (1.70 g, 10 mmol), hydrobromic acid (48.5%, 0.25 mL, 2 mmol), and water (2.5 mL) were heated at reflux for 75 minutes, to provide a solution of 2-bromoacetaldehyde. The solution was cooled to room temperature, and sodium acetate (0.50 g) added. The resulting solution was added over 3 hours to a stirred mixture of methyl 3-methoxycarbonyl-2-pyrrolidinylidenecarboxylate (1.00 g, 5 mmol), sodium acetate (3.10 g), and water (2 mL) in methanol (10 mL). The mixture was stirred an additional hour, and most of the solvents then removed by vacuum evaporation. The residue was dissolved in dichloromethane (100 mL), and the solution washed with aqueous sodium bicarbonate (2×25 mL) and dried over anhydrous magnesium sulfate. Removal of the solvent by evaporation gave 1.26 g of dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate.

B. Substituting 2-chloroacetaldehyde diethyl acetal for 2-bromoacetaldehyde diethyl acetal, and using a similar procedure to that in part A of this Example, one obtains

dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate.

C. Similarly, substituting other (lower alkyl) 3-(lower alkoxy)carbonyl-2-pyrrolidinylidenecarboxylates, such as ethyl 3-ethoxycarbonyl-2-pyrrolidinylidenecarboxylate, n-propyl 3-propoxycarbonyl-2-pyrrolidinylidenecarboxylate, etc., for the equivalent materials in parts A and B of this Example, one obtains other di(lower alkyl) 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylates, such as diethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate, di(n-propyl) 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate, etc.

EXAMPLE 5 Preparation of 2,3-dihydro-1H-purrolo[1,2-a]pyrrole-1,7-dicarboxylic acid.

A. Dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate (1.26 g, 5 mmol) and sodium hydroxide (1.00 g, 25 mmol) were heated in water (10 mL) at reflux for 1 hour. The resulting solution was cooled to 0° C. and acidified with hydrochloric acid (12 M) to pH 1. 2,3-Dihydro-1H-pyrrolo-[1,2-a]pyrrole-1,7-dicarboxylic acid (0.70 g, 71.4% yield) was collected by filtration and dried.

B. Similarly, substituting for the dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate of part A of this Example,

diethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate,

and similar di(lower alkyl) 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylates, one obtains

2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylic acid. 

We claim:
 1. A compound of formula XVI, ##STR9## in which each R is independently lower alkyl.
 2. The compound of claim 1 wherein each R is CH₃, C₂ H₅, or n--C₃ H₇.
 3. The compound of claim 2 wherein each R is CH₃. 